DE69305483T2 - Extrusion process - Google Patents

Abstract

A process for plastically extruding a fat-containing confectionery material e.g. chocolate which comprises feeding the fat-containing confectionery material into an extruder barrel (10) and applying pressure of a piston (11) to the fat-containing confectionery material in a substantially solid or semi-solid non-pourable form upstream of a flow constriction of a die (13) at a temperature at which the fat-containing confectionery material is extruded substantially isothermally and remains in a substantially solid or semi-solid non-pourable form to produce an axially homogeneous extruded product having a cross section that is of substantially the same profile as the die exit of the extruder.

Description

The present invention relates to a continuous or batch extrusion process, in particular to a process for extruding and shaping chocolate or fatty confectionery material in a solid or semi-solid state.

Fatty confectionery material may contain sugar, milk-derived components, fat and solids of vegetable or cocoa origin in varying proportions with a moisture content of less than 10% by weight, more often less than 5% by weight.

Dark chocolate is obtained by mixing sugar, cocoa butter (and other fats if desired) and cocoa mass. Milk chocolate contains milk fat and non-fat milk solids as additional ingredients. White chocolate contains milk fat and non-fat milk solids, sugar and cocoa butter (and vegetable fat if desired) without the addition of cocoa mass. The chocolate ingredients are usually mixed and ground to a paste before being conched at temperatures of 50º to 85ºC for a few hours to a few days, depending on the type of product and equipment used. The conched chocolate is then usually cooled by tempering to a temperature of usually about 28º-29ºC for milk chocolate and about 29º-30ºC for dark chocolate, at which temperatures the chocolate is still pasty and pourable and can be molded or used to coat confectionery centers. The tempered chocolate will become hard and non-pourable when cooled or left to stand at the final set temperature for a suitable period of time. When raising the temperature of chocolate which has already hardened and solidified by tempering and cooling after tempering to temperatures of the order of 28º-30ºC, the chocolate will still be solid and not pasty or pourable as it is immediately after tempering. In the present invention, "chocolate in a solid or semi-solid non-pourable state" means chocolate which has been cooled in the usual manner after conching to become hard and solid, either without tempering or by tempering and subsequent cooling or leaving to stand for a suitable period of time.

When the temperature of chocolate is gradually increased from 0ºC, it softens due to partial melting of the fats surrounding the particulate material until at about 30º-35ºC, depending on the chocolate composition, the chocolate begins to flow and has a viscosity sufficiently low to be poured.

GB-A-223362 (FR-A-570732) describes a process for forming chocolate containers by forcing solid chocolate mass under high pressure through an extrusion die and maintaining the temperature of the chocolate caused by friction during compression in the extrusion die so that the chocolate is extruded in a hard dense non-porous mass in the form of a tube. It is stated that the high extrusion pressure develops considerable heat but that the extruded product should retain the shape it has when it leaves the extrusion die.

GB-A-385571 describes a process for the manufacture of tubular chocolate pieces, in which a moderately heated chocolate mass is formed in a tube press, similar to that used for pressing cold macaroni and sponge cake doughs, fitted with a heating jacket, the tubes emerging from the dies being so rigid that no subsequent change occurs on cooling.

FR-A-628815 (corresponding to GB-A-281502) describes the production of moulded chocolate and states that the starting chocolate is flowable and pourable (p. 3, lines 32-32), cooling is carried out (p. 3, lines 90-91 and p. 4, lines 1-7), the initially moulded chocolate is in a molten or viscous state (claim 2), and does not specify any temporary flexibility or plasticity.

US Patent 1628251 describes a process for forming chocolate confectionery in elongated form, which process consists in passing the cold solid chocolate composition through a nozzle under sufficiently high pressure to form a continuous piece of chocolate which retains the shape given to it by said nozzle. On page 1, lines 35 to 35, it is stated that the Chocolate is hard and firm enough for shipping after leaving the nozzle.

US Patent 1649307 describes a method of manipulating chocolate which consists of forming it into the desired shape by pressure while maintaining the chocolate below the temperature at which it liquefies. An apparatus described on page 5, lines 71 to 88 uses forming members having a constricted portion emanating into a nozzle and it is stated that when the formed product exits the nozzle it shows no tendency other than to maintain the shape given by the forming member.

It is quite clear that in all of the above patents describing the extrusion of chocolate at a temperature below its melting or pouring point, the chocolate exits the extruder exit in a hard or rigid form. None of these patents mentions any flexibility or the possibility of plastically deforming the cold extruded chocolate immediately after extrusion. Furthermore, none of these patents mentions a continuous process, co-extrusion or immediately following direct injection molding of the extruded non-pourable product into a downstream mold.

We have now developed a process and surprisingly found that solid or semi-solid non-pourable chocolate can be plastically extruded to produce a solid or semi-solid non-pourable product having substantially the same profile as the nozzle exit of the extruder, which product has a temporary flexibility which can last for up to several hours before being lost. As a result of this temporary flexibility, plastic deformation or physical manipulation of the extrudate is possible before the flexibility is lost. In addition, our process can be carried out continuously, co-extrusion with other food materials is possible and the extruded product can be directly injection moulded.

According to the present invention, a process for plastically extruding a fat-containing confectionery material which comprises feeding the fatty confectionery material having a moisture content of less than 10% into an extruder and applying pressure to the fatty confectionery material in a solid or semi-solid, non-pourable state upstream of a flow restriction at a temperature of 0°C to 35°C, a pressure of 1 to 1,000 bar, a contraction ratio of greater than 1.5 and an extrusion speed of greater than 0.1 cm/s so that the fatty confectionery material is extruded and remains in a solid or semi-solid, non-pourable state to form an axially homogeneous extruded product having a cross-section with the same profile as the exit of the flow restriction, which is capable of retaining its shape and which has a temporary flexibility or plasticity which enables it to be physically handled or plastically deformed before it loses its flexibility or plasticity.

During the extrusion of the solid or semi-solid fatty confectionery material, the temperature of the fatty confectionery material may rise or fall if external heating or cooling means are present. The temperature remains substantially unchanged from the inlet to the exit of the flow restriction under the conditions of extrusion (i.e. temperature, pressure, contraction ratio and extrusion speed) if no external heating or cooling means are present, i.e. the extrusion is substantially isothermal in this case. The use of external heating or cooling means is not precluded as long as the material to be extruded remains in a solid or semi-solid, non-pourable state throughout the extrusion from the inlet to the exit of the flow restriction. In other words, the extrusion process itself does not cause a significant rise in the temperature of the fatty confectionery material. The physical state of the fatty confectionery material is such that its general deformation behavior during extrusion is more plastic in nature than that of a viscous liquid.

The fatty confectionery material can, if desired, be dark, milk or white chocolate.

The flow restriction in the extrusion process can be any constriction of the cross-sectional area of a pipe, but is usually a nozzle.

Extrusion may be induced by differential pressure across the flow restriction. This may be carried out, for example, by a piston extruder suitably operating at a controlled speed or pressure. The extruder may be, for example, a Davenport extruder, a constant pressure extruder, a single screw extruder, a twin screw extruder or a conform machine. The extrusion process may be continuous or batch.

The fatty confectionery material is preferably fed into the extruder barrel in a solid or semi-solid state. However, the material is extruded in a solid or semi-solid non-pourable state. The fatty confectionery material may be in a granular or continuous state. When in a granular state, the granular nature of the fatty confectionery material appears to be lost during extrusion to yield a substantially uniform material.

The extrusion temperature may be from as low as 0ºC to 35ºC, depending on the composition, in particular on the amount and type of fat present. When dark chocolate is used as the feedstock, the extrusion temperature may be from 10º to 34ºC, more usually from 15º to 32ºC, preferably from 18º to 30ºC and more preferably from 20º to 27ºC. In the case of milk chocolate, the extrusion temperature may be from 10º to 30ºC, more usually from 15º to 28ºC, preferably from 18º to 27ºC and more preferably from 20º to 26ºC. It will be understood that in this invention, when the chocolate is extruded at a temperature of 28º to 34ºC, it is in a solid or semi-solid, non-pourable state after it has hardened, as opposed to chocolate which has not been hardened, such as recently tempered chocolate which has not been hardened and is still pasty and pourable at such temperatures.

The extrusion process necessarily involves some kind of deformation between the inlet and the outlet of the extrusion system. The convergence or contraction ratio in any Extrusion opening or flow restriction is preferably greater than 1.5, where the convergence or contraction ratio is defined as the ratio of the inlet cross-section to the smallest cross-section of the nozzle for a simple cylindrical extrusion geometry.

During extrusion it is important that the fatty confectionery material does not become pourable and the extrusion temperature and pressure should be kept below a level where this could occur.

The extrusion pressure depends, among other things, on the contraction ratio, the extrusion temperature and the confectionery composition and can be from 1 to 1,000 bar, e.g. from 5 to 500 bar and typically from 5 to 250 bar.

A feature of the extrusion process is that the extrusion speed for a given nozzle configuration and material composition is only slightly dependent on the extrusion pressure.

The cross-sectional geometry of the nozzle can be square or profiled. Typically it can be a conical inlet with an inlet cone angle of 10º to 90º. The flow rate of the chocolate through the extruder nozzle will depend on extrusion pressure, temperature, nozzle configuration and material formulation, among other factors. For example, extrusion speeds can vary from 0.1 cm/sec to over 1 m/sec.

A wide variety of die shapes can be used and the extruded fatty confectionery material can have a solid profiled or hollow cross-section and have substantially the same shape as the die, e.g. rods, spirals, braids, springs, hollow cross-sections such as tubes and more complex shapes such as the letters of the alphabet as well as thin films with a thickness which can be as low as 100 µm. The dimensions of the die can depend on the desired size of the extruded product. A multi-hole die head can also be used if desired. Multi-material co-extrusion is also possible with this technology and the extrusion of the fatty confectionery material can be carried out as a co-extrusion with other food materials. Co-extrusion with other food materials such as ice cream, fondant, etc. is particularly advantageous when the fatty confectionery material is extruded into a hollow or tube shape.

Whilst flow restriction is necessary to extrude and plasticise the material, this can be an integral part of an injection mould, in which case the final shape of the product would conform to that of the mould, e.g. hollow shells, solid shapes, etc. This embodiment is particularly useful when the fatty confectionery material is extruded in a rigid profiled shape. Injection moulding is much easier to control and there is significantly less material loss compared to normal injection moulding using a molten material. In addition, unlike most other injection moulding processes, the final product does not require cooling and can be packaged directly.

Injection moulding may be achieved at processing temperatures similar to those described above for our extrusion process and the extrudate, e.g. chocolate, is extruded through a flow restriction which may form the injection nozzle of the injection moulding machine. In one embodiment, the chocolate may flow into a mould within channels of the mould and subsequently through a narrow sprue, e.g. from 100 to 500 µm. The chocolate is extruded into the mould as a flexible thread of semi-solid chocolate. As extrusion progresses, the mould progressively fills with chocolate due to the post-extrusion flexibility of the chocolate until the mould is completely filled. At this point the pressure within the mould is sufficient to allow complete consolidation of the chocolate. When this point is reached, no further flow occurs and the extrusion pressure can be released. At this point the mould can be opened and the injection moulded structures can be removed from the mould either mechanically or, for example, under vacuum. In this embodiment, the final product has essentially the same temperature as the feed material and therefore, unlike most other injection molding processes, no cooling period is required immediately after injection molding. The temperature of the mold can be varied within a wide range temperature range, but is suitably approximately the same as the extrusion temperature within the ranges described hereinbefore for the extrusion process. The injection molding process may further comprise multi-feed injection into molds using different components in each feed stream. In addition, the process may be used for coating centers which are positioned in the empty mold prior to injection molding. The injection molding process may be fully automated if desired.

The extruded product retains good sensory properties and, although it initially retains the shape of the extrusion die, it has post-extrusion flexibility or plasticity which can last up to several hours before being lost. For example, the flexibility can last for 4 hours or more, such as from 1 minute to 2 hours and more commonly from 5 minutes to 1 hour. Due to the extrusion of chocolate below its melting point, there is no need for cooling tunnels, the product can be packaged directly and it is possible to achieve precise weight control. In addition, due to the flexibility or plasticity of the extrudates, physical manipulation or plastic deformation is possible before the flexibility or plasticity is lost, e.g. bending, tying into knots, of the extrudates downstream of the die, allowing the formation of more complex shapes of the final product than the extrusion die profile. The present invention further provides the use of an extruded fat-containing confectionery product obtainable by the process of the present invention, which is capable of retaining its shape and which has temporary flexibility or plasticity, for physical manipulation or plastic deformation before it loses its flexibility or plasticity. This technology can further be used in conjunction with other processes, such as injection molding, to yield defined shaped products.

The following examples further illustrate the present invention.

example 1

Milk chocolate buttons were fed into the barrel of a Davenport extrusion rheometer, the barrel having been modified to provide a side-mounted pressure transducer just above the extrusion die. The barrel diameter was 19.5 mm and the chocolate buttons were allowed to equilibrate at the extrusion temperature of 24ºC. The material was then fed at a pressure of 50 bar through a die with a circular cross-section of 4 mm diameter and 8 mm length and an entrance angle of 45º. Smooth continuous extrusion was obtained for two samples at flow rates of 16 mm/sec as shown in the accompanying Figures 1 and 2. The extruder 1 is shown in Figures 6 and 7, which show a cylinder 10, a piston 11, a pressure transducer 12, an extrusion nozzle 13 with the length L, a nozzle outlet 13a, a cross section D and an entry angle and a fastening nut 14.

These figures show the time course of the pressure profile during extrusion. After an initial flow pressure is reached, the extrusion pressure drops to an essentially constant value. After flow stops (after approximately 180 sec in Figure 1), the extrusion pressure relaxes.

A solid non-castable rod-shaped product was obtained which retained its shape but was flexible for 30 min, during which period it could be bent or twisted into knots before it hardened.

Example 2

A similar procedure to that described in Example 1 was followed, except that the extrusion temperature was 28°C. The results for two samples are shown in the accompanying Figures 3 and 4.

Example 3

A similar procedure to that described in Example 1 was followed, except that the extrusion temperature was 18°C. The results are shown in Figure 5.

Example 4

Using a hydraulically driven piston under a substantially constant pressure, the Chocolate mass extruded through a small orifice showed a weak dependence on the differential pressure across the die, which was characterized by a logarithmic-linear relationship when extruded through an orifice with a diameter of 4 mm at flow velocities between 1 and 100 cm/sec.

Example 5

Using the method described in Example 4, chocolate was extruded through a 4 mm die at various temperatures, requiring the following pressures to achieve similar output rates:

Example 6

A procedure similar to that described in Example 1.

Example 4 was followed except that the opening was replaced by a slot measuring 1 mm x 20 mm. A solid, non-pourable, flexible thin chocolate ribbon was formed at flow velocities of 1 to 100 cm/sec.

Example 7

A hydraulically driven Florin piston extruder 2 is shown in Figure 8 and comprises a barrel 15, a hydraulically driven piston 16, a feed opening 17, an extrusion nozzle 18 having a nozzle exit 18a with a cross section of 4 mm diameter and an internal cylinder diameter of 25 mm. Chocolate buttons were dropped into the feed opening after which the piston was advanced hydraulically under a pressure of 80 bar and at a temperature of 23°C. Semi-continuously, solid non-pourable rods 19 of 4 mm diameter were produced which retained their shape and had an initial flexibility lasting for 40 minutes.

Example 8

A Florin extruder 2 similar to that shown in Figure 8, but with a centrally located "torpedo" 20 positioned in the barrel, is illustrated in Figure 9. The nozzle 18 has a nozzle exit 18b. The same procedure as in Example 7 was followed, but instead of rods, solid non-castable hollow tube sections 21 were produced, having an outside diameter of 10 mm and an inside diameter of 6 mm. The tubes had a post-extrusion flexibility which lasted for about 1 hour.

Co-extrusion with fondant can also be carried out using a "torpedo" equipped with a longitudinal channel through which the fondant flows to produce a chocolate-coated fondant.

Example 9

A Florin piston extruder similar to that shown in Figure 8, but with a nozzle having a cross-section of 5 mm diameter, was adapted to form the injection nozzle of an injection molding machine as shown in Figure 10. Injection molding of the chocolate was carried out with the temperature of both the extruder and the mold at 250°C, while simultaneously pressurizing the piston to 80 bar and clamping the split mold using hydraulic pressure. The semi-continuous rods 22 flowed within the channels 23 and then through the narrow sprues 24, each having a width of 200 µm, into the hollow sphere molds 25, each having a diameter of 12 mm. The chocolate was extruded into each mold as a flexible thread of semi-solid chocolate. As extrusion continued, the mold gradually filled with chocolate until the entire mold was filled. At this stage, the pressure within the mold was sufficient to allow complete consolidation of the chocolate to occur. Once this point was reached, no further flow occurred and the extrusion pressure was released. The mold was then opened and the injection molded chocolate parts were mechanically removed from the mold. Unlike most injection molding processes, it was not necessary to cool the product immediately after injection molding and the product could be packaged directly.

Claims (25)

1. A method for plastically extruding a fatty confectionery material, which comprises feeding the fatty confectionery material having a moisture content of less than 10% by weight into an extruder (1, 2) and applying pressure to the fatty confectionery material in a solid or semi-solid, non-pourable state upstream of a flow restriction (13, 18) at a temperature of 0°C to 35°C, a pressure of 1 to 1,000 bar, a contraction ratio of greater than 1.5 and an extrusion speed of greater than 0.1 cm/s, so that the fatty confectionery material is extruded and remains in a solid or semi-solid, non-pourable state to form an axially homogeneously extruded product (19, 21) having a cross-section with the same profile as the exit (13a, 18a, 18b) of the flow restriction, which is capable of maintaining its shape and which has a temporary flexibility or plasticity that enables it to be physically handled or plastically deformed before it loses its flexibility or plasticity. 2. A process according to claim 1, wherein the extrusion temperature is from 0º to 35ºC. 3. A process according to claim 1, wherein when the fatty confectionery material is dark chocolate, the extrusion temperature is from 15º to 32ºC. 4. A process according to claim 3, wherein the extrusion temperature is from 18º to 30ºC. 5. A process according to claim 1, wherein when the fat-containing confectionery material is milk chocolate, the extrusion temperature is from 15º to 28ºC. 6. A process according to claim 5, wherein the extrusion temperature is from 18º to 27ºC. 7. The method of claim 1, wherein the convergence or contraction ratio in any extrusion orifice or flow restriction exit is greater than 1.5. 8. The process of claim 1, wherein the extrusion speed is from 0.1 cm/sec to 1 m/sec. 9. The process according to claim 1, wherein the extrusion pressure is from 1 to 1,000 bar. 10. A process according to claim 1, wherein the extrusion temperature and pressure are maintained below a level that would cause the fat-containing confectionery material to become pourable. 11. Method according to claim 1, wherein the cross-sectional geometry of the flow constriction (13, 18) is of square or profiled shape. 12. The method of claim 1, wherein the flow restriction (13, 18) has a conical inlet with an inlet cone angle of 10° to 90°. 13. The method of claim 1, wherein the extrudate (19, 21) has a hollow or profiled cross-section. 14. A process according to claim 1, wherein the extrusion of the fat-containing confectionery material is carried out as a co-extrusion with other food materials. 15. A process according to claim 14, wherein the fatty material is extruded in tube form. 16. The method of claim 1, wherein the extrudate (19) from the outlet of the flow restriction (13, 18) is filled either directly or indirectly into a mold (25) to form a molded product. 17. The method according to claim 16, wherein the outlet of the flow restriction (13, 18) forms the injection nozzle of an injection molding machine. 18. A method according to claim 16, wherein the extrudate (19) is filled into the mold (25) at a temperature similar to the temperature used in the extrusion process according to claim 1. 19. A method according to claim 18, wherein the extrudate is chocolate injected through a sprue (24) having a width of 100 to 500 µm. 20. The method of claim 16, wherein the molded product is at substantially the same temperature as the extrudate. 21. The method of claim 16, wherein the molding process comprises multi-feed injection into molds using different components in each feed stream. 22. A method according to claim 16, wherein centers are positioned in the empty mold before the extrudate is injected into the mold to coat the centers. 23. A process according to claim 1, wherein after extrusion, physical manipulation or plastic deformation of the extrudate is carried out downstream of the die. 24. A process according to claim 1, wherein the temperature of the fat-containing confectionery material remains substantially unchanged during the extrusion process. 25. Use of an extruded fat-containing confectionery product obtainable by a process according to any one of the preceding claims and capable of retaining its shape and having a temporary flexibility or plasticity for physical manipulation or plastic deformation before loss of its flexibility or plasticity.